The Ras family of proteins are important in the signal transduction pathway modulating cell growth. The protein is produced in the ribosome, released into the cytosol, and posttranslationally modified The first step in the series of post-translational modifications is the alkylation of Cys.sup.168 with farnesyl or geranylgeranyl pyrophosphate in a reaction catalyzed by prenyl transferase enzymes such as farnesyl transferase and geranylgeranyl transferase (Hancock, J F, et al., Cell 57:1167-1177 (1989)). Subsequently, the three C-terminal amino acids are cleaved (Gutierrez, L., et al., EMBO J. 8:1093-1098 (1989)), and the terminal Cys is converted to a methyl ester (Clark, S, et al., Proc. Nat'l Acad. Sci. (USA) 85:4643-4647 (1988)) Some forms of Ras are also reversibly palmitoylated on cysteine residues immediately N-terminal to Cys.sup.168 (Buss, J E, et al., Mol. Cell. Biol. 6:116-122 (1986)). It is believed that these modifications increase the hydrophobicity of the C-terminal region of Ras, causing it to localize at the surface of the cell membrane. Localization of Ras to the cell membrane is necessary for signal transduction (Willumsen, B M, et al., Science 310:583-586 (1984)).
Oncogenic forms of Ras are observed in a relatively large number of cancers including over 50 percent of colon cancers and over 90 percent of pancreatic cancers (Bos, J L, Cancer Research 49:4682-4689 (1989)). These observations suggest that intervention in the function of Ras mediated signal transduction may be useful in the treatment of cancer.
Previously, it has been shown that the C-terminal tetrapeptide of Ras has the "CAAX" motif (wherein C is cysteine, A is an aliphatic amino acid, and X is any amino acid). Tetrapeptides having this structure have been shown to be inhibitors of prenyl transferases (Reiss, et al., Cell 62:81-88 (1990)). Poor potency of these early farnesyl transferase inhibitors has prompted the search for new inhibitors with more favorable pharmacokinetic behavior (James, G L, et al., Science 260:1937-1942 (1993); Kohl, N E, et al., Proc. Nat'l Acad. Sci. USA 91:9141-9145 (1994); deSolms, S J, et al., J. Med. Chem. 38:3967-3971 (1995); Nagasu, T, et al., Cancer Research 55:5310-5314 (1995); Lerner, E C, et al., J. Biol. Chem. 270:26802-26806 (1995); Lerner, E C, et al., J. Biol. Chem. 270:26770 (1995); and James, et al., Proc. Natl. Acad. Sci. USA 93:4454 (1996)).
Recently, it has been shown that a prenyl transferase inhibitor can block growth of Ras-dependent tumors in nude mice (Kohl, N E, et al., Proc. Nat'l Acad. Sci. USA 91:9141-9145 (1994)). In addition, it has been shown that over 7 percent of a large sampling of tumor cell lines are inhibited by prenyl transferase inhibitors with selectivity over non-transformed epithelial cells (Sepp-Lorenzino, I, et al., Cancer Research, 55:5302-5309 (1995)). Inhibiting farnesylation has been disclosed as a method of treating hepatitis delta virus infection, (Casey, P, et al., WO 97/31641).